Discharge apparatus



atented Jan. 12, 1943 DISCHARGE APPARATUS Pennsylvania Originalapplication August 1'7, 1938, Serial No. 225,368. Divided and thisapplication August 5, 1941, Serial No. 405,473

7 Claims.

.My invention relates to electric discharge apparatus and has particularrelation to discharge apparatus for controlling the supply of current toa load requiring power in intermittent pulses such as a resistance spotand seam welding load, for example.

This application is a division of application, Serial No. 225,368, filedAugust 17, 1938.

The present invention also relates to an application Serial No. 214,160,filed June 16, 1938, by me and Russell W. Staggs, and assigned to theWestinghouse Electric 81 Manufacturing Company, and is an extension ofthe invention disclosed therein.

In the last-mentioned application, apparatus is disclosed thatincorporates electric discharge valves of theimmersed-ignition-electrode type through which current is generallysupplied from an alternating current source to a load requiring power inintermittent pulses. By the proper selection of the ignition electrodesof the discharge valves, and by the proper adjustment of the circuit inwhich they are connected, the load current variations are maintainedwithin limits as regards both the current-time product and the magnitudeof the individual sub-impulses which form a main impulse.

As is explained in the aforesaid application, the load supplied in thepractice of the invention disclosed often has a poor power factor andthe supply of the pulses is initiated at random. The magnitude of thevariations produced is dependent on the'relationship between the anglein the halfcycles of the source at which the valves are renderedconductive and the angle at which current zero occurs. The former Ishall designate herein as the ignition angle, the latter as the powerfactor angle.

In accordance with the invention disclosed in the aforesaid application,variations'in the 'current-time product and the magnitudes of thesubimpulses are limited by so selecting theigniticn electrodes and theircircuits that the ignition angle is of the same order of magnitudeas thepower factor angle. However, no simple means is made available inaccordance with the said invention for adjusting the ignition angle withany degree of precision at a definite value and no simple contrivancefor varying the current flow through the load overawide range isprovided.

It is, accordingly, an object of the present invention to provide anarrangement of simple structure in accordance withthe aforesaidapplication, in which the ignition angle shall be ad- .justable at will.

A more general object of my inventionisto provide a control systemincorporating an electric discharge valve of the immersed ignitionelectrode type, in which the instant at which the valve is renderedconductive shall be adjustable'at will by the proper adjustment of theignitioncircuit.

Another general object of my invention is to provide an arrangement ofsimple structure for supplying a load from an alternating source whereinthe supply of power shall be initiated at instants inthe half periods ofthe source which may be selected at will.

Still another general object of my invention is to provide apparatus forsupplying a load from an alternating current source through electricdischarge valve means of the immersed ignition elec trode 'type, inwhichthe impedance of the ignition circuit shall be varied at will to varythe instants in the half periods of the source at which the valve meansis rendered conductive.

A more specific object of my invention is to provide a resistance spotand seam welding system of simple structure incorporating the feature ofheat control.

'A still further object of my invention is to provide an electricdischarge valve of the immersed ignition electrode type that shall beparticularly adaptable for use in apparatus in which the ignitionelectrode is to be supplied continuously or for relatively longintervals of time with current when the valve is in operation.

More concisely stated, it is an object of my invention to provide simpleand tractable apparatus for supplying current to a load requiring powerin intermittent pulses, by the operation of which the magnitude of thepulses supplied shall be variable over a wide range.

According to my invention, the ignition potential for the electricdischarge valves is derived from the same source as the anode-cathodepotential. However, in the ignition circuit impedance means, such asvoltage dividers, variable reactors or other induction regulators areinterposed to properly set the ignition potential supplied to attain thedesired ignition characteristics.

Thenovel features that I consider characteristic of my invention are setforth withparticularity in the appended claims. The invention itself,however, both as to its organization and its method of operation,together with additional objects and advantages thereof, will best beunderstood from the following description of specific embodiments whenread in connection with the accompanying drawing, in which:

Figure l is a diagrammatic view showing an embodiment of my invention;

Fig. 2 is a diagrammatic view showing a modification of my invention;

Fig. 3 is a diagrammatic view showing a further modification of myinvention; and

Fig. 4 is a diagrammatic view showing still another modification of myinvention.

The apparatus shown in Fig. 1 is a resistance seam welding systemcomprising a welding transformer 9 from the secondary ll of whichcurrent impulses are supplied to a material 13 to be welded through apair of welding electrodes [5. The primary ll of the Welding transformeris connected to a suitable source l9 of alternating current, which maybe an ordinary commercial BO-cycle source, through a pair of electricdischarge valves EI and 23 of the immersed ignition electrode type. Eachof the valves has an anode 25 composed of nickel, carbon or othersuitable material, a cathode 21 consisting of a pool of mercury or likematerial, and an ignition electrode 29 composed preferably of boroncarbide but in certain cases also of silicon carbide or other materials.The valves 2| and 23 are connected between the source l9 and the load9I3 in anti-parallel.

In seam welding apparatus, the current is supplied in the form ofdiscrete impulses; each impulse consists of a, train of sub-impulses,one sub-impulse flowing during each half period of the source. Tomeasure out the welding current impulses, a timing system 3| comprisinga direct current motor 33 which is supplied from the source 19 through arectifier 35 and which drives a commutator 31 is provided. Thecommutator 31 is provided with an inner completely conducting ring 39and an outer ring 4| in metallic engagement with the inner ring. Theouter ring ll has an insulating segment 43 extending over a portion ofits periphery and a conducting segment 45 extending over the remainder.Brushes 41 and d9 engage the inner and outer rings 43 and t5,respectively, and are, in turn, connected in a circuit including asuitable circuit closing element which may be a foot switch, a pushbutton, or the like.

When power is supplied to the system and the switch 51 is closed, acircuit through the primary 63 of an ignition transformer 65 is closedand opened wth a periodicity dependent on the speed of rotation of thecommutator 31 and for intervals, depending on the relative lengths ofthe conducting and insulating segments. The circuit extends from thelower terminal 6! of the source l9 through the primary I! of the weldingtransformer 9, a conductor 69, the switch 51. the conducting segment 65of the commutator 31, a conductor 1 l the adjustable tap 13 of theprimary B3 of the ignition transformer 65, the selected turns of theprimary 63, a conductor 15, a conductor Tl, to the upper terminal 19 ofthe supply source.

The primary 63 of the ignition transformer 85 is thus connected acrossthe electric discharge valves 2| and 23, and when the latter are notcarrying current, the potential of the source is impressed between itsterminals. The transformer 65 is provided with a pair of secondaries 8!and 83. the former 3| being directly connected between the ignitionelectrode 29 and the cathode 21 of the discharge valve 2! and the letter83 being directly connected between the corresponding electrodes of theother Valve 23. Accordingly, when the ignition transformer 85 isenergized by the source, a potential is impressed across the ignitionelectrodes 29 of the valves 2| and 23. For a predetermined polarity ofthe source potential, one or the other of the ignition electrodes 29 issupplied with a positive half wave of potential at the same time thatpositive anode-cathode potential is impressed on its valve 2| or 23. Theohmic resistance of the ignition electrode is large as compared to thereactive impedance in the ignition circuits and, therefore. theanode-cathode potential and the potential impressed on the ignitionelectrode may be assumed to be in phase. When during any positivehalf-cycle the potential across one ignition electrode 29 rises to asulficiently high value, the corresponding valve is rendered conductive.After the valve becomes conductive, the potential across the primary 63of the control transformer is reduced to the arc drop value, which is ofthe order of 10 to 20 volts and, therefore, the flow of substantialcurrent through the ignition electrode is interrupted. As the sourcepotential varies in polarity, the valves 2| and 23 are alternatelyrendered conductive and alternating current pulses are supplied to thematerial to be welded in rhythm with the half-cycles of the source.

Impulses made up of trains of half-cycle sub impulses are thus suppliedfor intervals of time determined by the length and the speed of rotationof conducting segment 55 of the commutator 31. The number ofsub-impulses which make up an impulse and, therefore, the time of supplyof each Welding impulse or the number of welds per unit time, may bevaried or regulated by controlling the speed of the motor 33. The latterobject is accomplished in a simple manner by varying the resistance inthe field circuit 81 of the motor. The time between impulses is, ofcourse, dependent on the length and speed of the insulating segment 4-3.The ratio of the welding time to the pause may be varied by varying therelative lengths of the conducting and insulating segments 45 and 53.The measuring out of a predetermined number of sub impulses to make up awelding impulse is known in the art as the timing of the supply ofwelding current. In addition to the timing, another desideraturn inwelding is heat control, i. e., the control of the heating of thematerial to be welded during the welding operation.

The heat supplied by the welding current is dependent on the magnitudeof the welding current which flows and. therefore, on the magnitude ofthe sub-impulses. In the present case, the magnitude of the sub-impulsesis dependent on the angle in the half-cycles of the source at which thesub-impulses current flow is initiated and this angle, in turn, issimply the ignition angle. To control the heat supplied during welding,therefore, the ignition angle is controlled. This object may beaccomplished by setting the amplitude of the ignition potential at thedesired values; that is to say, by engaging the movable tap 13 with theproper fixed tap 89 of the ignition transformer secondary 63.

I have found that if an ignition electrode 29 is continuously, or forrelatively long time intervals, supplied with current, it may becomedeteriorated by reason of the heat developed by the flow of current. Inthe embodiment of my invention disclosed in Fig. 1, this undesirablefeature is eliminated by the connection of the primary B3 of theignition transformer 65 in such manner that its potential is reduced tothe are drop value when the load is rendered-ponductive.

In the modification disclosed inFig. 2, the ignition transformer 65 isreplaced by a voltage divider consisting of a pair of variablereactors9| and 93. One of the reactors 93 isconnec'ted at one of its terminals"95 to the common junction point 9'! of the terminal :79 of the sourceland the cathode '2? of one of the valves 23, and at its other terminal99 to one of the fixed contacts of the switch 51. The other reactor SIis con nected at one terminal lfil to the common junction point of theterminal Hi3 of the primary I! of the welding transformer 9 that isremote from the source 19 and the other cathode 21 and at its otherterminal m to the remaining fixed contact of the switch 51. The movabletaps I01 and H39 of the reactors 9| and 93, respectively, are connectedeach to an ignition electrode 29 of valves 2! and 23, respectively. Whenthe push button 5! is closed, potentials determined 'by the setting ofthe adjustable contacts I91 and I69 of the voltage divider 9 I-93 areimpressed across the ignition electrodes 29 and the valves are renderedconductive at instants in the half periods of the source l9predetermined by the settings.

The Fig. 3 modification is similar to the Fig. 2 modification, exceptthat the voltage divider consists of a pair of resistance elements I51and 159 rather than a pair of reactance elements 9! and 93. The latterarrangement has the advantage that whatever phase displacement betweenthe source potential and the potential impressed across the ignitionelectrodes may be introduced by reactors such as 9! and B3 is entirelyeliminated.

In the Fig. modification, the ignition electrodes are interconnectedthrough a rheostat l6| when the push button 5"! is closed. By reason ofthis interconnection, the ignition electrodes 29 are connected acrossthe source through the rheostat [8| when the valves are non-conductive.The potential drop across the ignition electrodes 29 is dependent on thesetting of the rheostat. For a predetermined setting of the rheostat,the potential impressed across the ignition electrodes 29 rises to theignition value at a predetermined point in the half periods of thesource. By the operation of the rheostat I61, therefore, the point ofignition in the half periods of the source may be set at will.

It is to be noted further that while my invention has been disclosedherein as applied in a seam welding system, it has general applicabilityand may be used wherever the supply of power to a load is to becontrolled. In particular, it may be used with advantage in a spotwelding system such, for example, as is shown in the above-mentionedapplication to Staggs and myself.

Further in the modifications, it is to be noted that While in thepreferred practice of my invention two distinct discharge valves areconnected in anti-parallel to pass alternating current, the use of asingle tube having two mercurypool cathodes with an ignition electrodeimmersed in each and two anodes is understood to be within the scope ofmy invention. When I use the expression in effect, a pair of valveshereinafter, I mean thereby both the two-valve arrangement as disclosed,and the single-tube arrangement just described.

Although I have shown and described certain specific embodiments of myinvention, I am fully aware that many modifications thereof are pos-"sible. My invention, therefore, is 'not to be 'restricted exceptinsofar as is necessitated bythe prior art and by the spirit of theappended claims.

I claim as my invention:

1. In combination, an electric discharge device of the immersed ignitionelectrodetype having a plurality of principal electrodes and a controlelectrode immersed in one of said principal electrodes, a source ofperiodically pulsating potential, means for impressing a potential fromsaid source between said principal electrodes, and voltage divider meansenergized from said source for impressing a potential across saidcontrol electrode to render said device conductive at instantspredeterminable at will.

2. For use in supplying a load from a source of alternating potential,the combination comprising in effect a pair of electric dischargedevices of the immersed-ignition electrode type each having a pluralityof principal electrodes and a control electrode immersed in one of saidprincipal electrodes interposed between said source and said load so asto transmit alternatin current to said load, voltage divider meanshaving a plurality of taps and connected in shunt with said devices, andmeans connecting the control electrode of each of said devices to a tapof said divider.

3. In combination, an electric discharge device of theimmersed-ignition-electrode type having a plurality of principalelectrodes and a control electrode immersed in one of said principalelectrodes, a source of periodically pulsating potential, means forimpressing a potential from said source between said principalelectrodes, and voltage divider means energized from said source forimpressing a potential in phase with said source across said controlelectrode to render said device conductive at instants predeterminableat will.

4. In combination, an electric discharge device of theimmersed-ignition-electrode type having a plurality of principalelectrodes and a control electrode immersed in one of said principalelectrodes, a source of periodically pulsating potential, means forimpressing a potential from said source between said principalelectrodes, voltage divider means connected in shunt with said principalelectrodes and having a plurality of taps, and means for connecting saidcontrol electrode to any one of said taps selected at will.

5. For use in supplying a load from a source of alternating potential,the combination comprising in effect a pair of electric dischargedevices of the immersed-ignition-electrode type, each having a pluralityof principal electrodes and a control electrode immersed in one of saidprincipal electrodes interposed between said source and said load so asto transmit alternating current to said load, resistance means connectedin shunt with the principal electrodes of said devices and having aplurality of intermediate taps, and means connecting the controlelectrode of each of said devices to a tap of said resistance means.

6. For use in supplying a load from a source of alternating potential,the combination comprising in efiect a pair of electric dischargedevices of the immersed-ignition-electrode type, each having a pluralityof principal electrodes and a control electrode immersed in one of saidprincipal electrodes interposed between said source and said load so asto transmit alternating current to said load, reactive means connectedin shunt with the principal electrodes of said devices and having aplurality of intermediate taps, and means connecting the controlelectrode of each of said devices to a tap of said reactive means.

7. In combination, an electric discharge device of theimmersed-ignition-electrode type having a plurality of principalelectrodes and a control electrode immersed in one of said prin- 10cipal electrodes, a source of periodically pulsat ing potential, meansfor impressing a potential from said source between said principalelectrodes, impedance means connected in shunt with said principalelectrodes and having a plurality of taps, and means for connecting saidcontrol electrode to any one of said taps selected at will.

EDWIN H. V'EDDER.

